On Jul 3, 2025, at 7:47 AM, Hans de Goede hansg@kernel.org wrote:
Hi Matthew,
On 3-Jul-25 3:54 AM, Matthew Schwartz wrote: Hello,
I installed kernel 6.15.4 to find that my battery estimate on my handheld gaming device was completely inaccurate, instead giving negative values and an unknown estimated battery life in multiple places.
After bisecting, I landed on "ACPI: battery: negate current when discharging” as the bad commit. This commit breaks not one but several userspace implementations of battery monitoring: Steam and MangoHud. Perhaps it breaks more, but those are the two I have noticed so far.
Thank you for reporting this.
As Rafael already indicated this patch will need to be reverted to unbreak userspace.
But, the patch was actually doing the right thing, according to:
Documentation/ABI/testing/sysfs-class-power
What: /sys/class/power_supply/<supply_name>/current_avg Date: May 2007 Contact: linux-pm@vger.kernel.org Description: Battery: ... Access: Read
Valid values: Represented in microamps. Negative values are used for discharging batteries, positive values for charging batteries and for USB IBUS current.(and the same for current_now)
and there are many power_supply fuel-gauge drivers (1) under drivers/power/supply/ which do adhere to this specification and report a negative current for discharging.
So if any of the userspace consumers of this API you mention were to run on hw with these drivers the same problem will be hit. Can you please file bugs against these userspace projects so that they can fix this?
Sure, I filed a bug with MangoHud last night about the kernel change breaking the current battery logic so I will mention this concern when updating that issue, and I will also file a new bug with Steam.
Thanks, Matt
Regards,
Hans
- For directly accessing fuel-gauge chips on devices where these
are directly accessible instead of being exposed through ACPI